An ink composition of this kind, which is also known as a hot melt ink, is known from U.S. Pat. No. 7,981,203. This patent describes a hot melt ink to be applied in ink jet printing devices, comprising a non-aqueous carrier, and at least one dye of which comprises at least one salt of the anthrapyridone series, in particularly the triphenylmethylphosphonium (TMP) salt of C.I Acid Red 143 and 143:1 are disclosed in said patent.
It is a disadvantage of the ink composition disclosed in U.S. Pat. No. 7,981,203 that if alkali metal ions and/or alkaline earth metal ions are present in the ink composition e.g. due to natural occurrence in raw materials, such metal ions may precipitate in the nozzles of the print head as an alkali metal salt or alkaline earth metal salt of the chromophores C.I. Acid Red 143 and 143:1. Examples thereof are magnesium and/or calcium salts of the above disclosed chromophores, in particular calcium salts thereof. Such nozzle depositions may cause jet angle defects and print quality problems (e.g. white stripes on prints).
In general, the above disadvantage relates to hot melt ink compositions comprising a salt of the anthrapyridone series as a dye, if at least one alkali metal cation or alkaline earth metal cation present in the ink composition has a stronger interaction with the chromophore anion than the cation that was originally associated with the dye anion. In such cases ion exchange of the cation associated with the chromophore anion occurs, possibly leading to nozzle depositions as explained above.
It is another disadvantage of the ink compositions disclosed in U.S. Pat. No. 7,981,203 that the solubility of such dyes in the ink compositions tends to be low, which may lead to crystallization of the dye at the desired concentration level of the dye in the ink composition. Dye crystals may cause filter and nozzle clogging.
The disadvantages particularly hold for ink compositions comprising magenta dyes.
It is therefore an object of the present invention to provide a hot melt ink composition which obviates or at least mitigates the above-described disadvantages.